High performance brushless motor and drive for an electrical vehicle motorization

ABSTRACT

The system includes a permanent magnet three-phase motor and an electronic current controlled inverter by pulse width modulation. The motor has twenty-two poles and twenty-four slots, three phases and a cylindrical outer rotor. This structure minimizes torque ripple and maximizes energy efficiently. All coil windings are wound around the stator teeth. A winding configuration is proposed. The motor phases are supplied by alternating rectangular current waveforms. A specific inverter control system is described to maximize efficiency and reduce current ripple and electromagnetic interference under motorizing or generating operations. The current control is realized by using the MOSFETs voltage for the current measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/937,936 filed Feb. 1, 2002 by Applicant now U.S. Pat. No. 6,630,764,which is a 371 of PCT/CA99/00290 filed Apr. 1, 1999.

FIELD OF THE INVENTION

The present invention relates to a low cost electric system composed ofa new DC brushless permanent magnet motor and its electronic drive whichprovides high efficiency operation and low torque ripple for themotorization of electric vehicles like, bicycles, rolling chairs,scooters, tricycles, golf cars, trolleys and small utility vehicles.

BACKGROUND OF THE INVENTION

The motor and its electronic system are supplied by one or severalbatteries. The vehicle wheel drive can be direct to maximize efficiencyor equipped with a speed reducer to minimize the motor size. Theproposed solution uses a permanent magnet three-phase motor which canreach four times the nominal torque. This motor structure includes anouter rotor which can be fitted into a vehicle wheel. It can be used asmotor or generator with energy recuperation in the battery duringbraking periods or to create electricity to recharge battery, or powerother devices by changing the motor. This motor structure is supplied bya PWM (Pulse Width Modulation) current controlled inverter. The operatorcan impose the machine torque level in motor or generator operation bysetting a current reference. The shape of the alternative phase currentwaveform is rectangular with a width of 120 electrical degrees. Thiskind of motor supply is the simplest to realize and it reduces the costof the control system and the number of sensors.

The brushless motor includes a cylindrical outer rotor wherein permanentmagnets are mounted on the surface and an internal stator with coils ofinsulated wire wound around the teeth. There are twenty-two magnet poleson the rotor alternatively magnetized north and south and twenty-fourslots on the stator. This combination of slots and poles for athree-phase motor structure allows the realization of a specialconcentrated winding around the teeth with only one coil per slot. Inthis case, there are only twelve coils to realize. The windingcoefficient and the copper filling factor are higher than in the otherknown solutions described by Konecny U.S. Pat. No. 4,774,428, Huang andal. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378which are using winding with two coils per slot.

This kind of winding with one coil per slot simplifies the assembling ofthe rotor position sensors (i.e. hall detectors) near the air gap. Thehall detector are fixed on the side of several teeth which have nowinding and they are using the leakage flux of the permanent magnets todetect the rotor position.

The proposed structure maximizes the energy efficiency and the motorstarting torque per unit volume of winding. The advantages of aconcentrated winding around the teeth in comparison with a classicaldistributed winding are described in Konecny U.S. Pat. No. 4,774,428 andPermanent magnet brushless DC motor with soft metal powder forautomotive application by J. Cros and P. Viarouge published in the IEEEIndustry applications Society in October 1998. The volume of copper isreduced and subsequently the Joule losses are minimized.

The amount of vibrations and the cogging torque ripple are reduceddrastically like in the other structure combinations described byKonecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196and Katsuma and al. U.S. Pat. No. 4,719,378. The least common multiple(LCM) of the motor's poles and slots describes how many peaks of coggingtorque will be present over a single revolution of the motor. In thiscase, there are 264 torque pulses per revolution and consequently, thecogging torque amplitude is very low (less than 3% of the rated torque).

The proposed motor structure also minimizes the net radial force likeanother structure described by Huang and al. U.S. Pat. No. 5,675,196.

Reference is made to British Patent GB 2 289 991 which discloses awinding sequence for a motor having twelve slots and ten poles. It isdescribed in that Patent the use of a structure and a specific windingsequence wherein one winding per slot is provided to obtain independentmagnetic flux flow for each phase.

Japanese Patent A-400 4703 relates to an electric bicycle mostspecifically to a system capable of detecting the direction of rotationof the rotor as well as its speed by the use of an optical sensorwhereby to control the amplitude of the current in the motor.

The electronic supply includes a power electronics supply and a currentcontrol electronics circuit. Both systems can be inserted inside themotor housing, in the center of the stator yoke. The power electronicssystem is composed of an inverter with six MOSFETs or multiple MOSFETswhich operate like six MOSFETs. The structure diodes of the MOSFETs areused to ensure the current reversibility. At each sequence of conductiondefined by the rotor position detector, two transistors are switched onto supply two motor phases. In the classical mode of operation, amodulation signal is applied on the gate of these two transistors. Thismethod simplifies the control realization and only one current sensorcan be inserted in the DC bus for the current measurement.

Another solution consists in applying the modulation signal on onetransistor only at each sequence of operation: this method is the singleswitch modulation technique. The other transistor is switched “on”during all the duration of this sequence of conduction. This mode ofoperation is described in E.M.I. tests on a brushless actuator:Comparison by M. Lajoie-Mazene and J. P. Berry published in EuropeanPower Electronics in September 1993, in the case of monitoring operationonly, compared to the classical mode of operation where the modulationsignal is applied on the gate of the two transistors. It is shown thatthe single switch modulation provides lower electromagneticinterferences (EMI) and reduces the commutation losses, the conductionlosses in low voltage applications, the current ripple and the size ofthe input filtering capacitor. The proposed electronic system is usingthe single switch modulation and it can be used for motor as well asgenerator operation. Consequently, the current regulation is realizedwithout any external current sensor.

Another article of interest is the Synthesis of high performance PMmotors with concentrated windings by J. Cros and P. Viarouge publishedin the IEEE Transactions on Energy Conversion in June 2002. It explainsa method for determining a winding for a concentrated winding motor.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide a high performancebrushless DC permanent magnet motor and a pulse width modulationelectronic inverter for the motorization of electric vehicles suppliedwith electrical batteries. The motor structure includes an outer rotorwhich can be fitted to a vehicle wheel. It can be used as a motor or asa generator with recuperation of kinetic energy in the batteries duringbraking periods.

Another feature of the invention is to provide a special design and thedesign of its three-phase winding maximize the energy efficiency and themotor starting torque per unit volume of winding. A concentrated windingis wound around the teeth with only one coil per slot. This solutionsimplifies the winding realization and maximizes the winding coefficientand the copper filling factor.

Another feature of the invention is that the assembling of the rotorposition sensor (i.e. hall detectors) near the air gap is simplified bythe winding configuration. The hall detector are fixed on the side ofseveral teeth which have no winding and they are using the leakage fluxof the permanent magnets to detect the rotor position. The amount ofvibrations, the cogging torque ripple and the radial force are greatlyreduced.

Another feature of the invention is to provide specific inverter controlsystem which reduces the commutation losses, the diode conduction lossesin low voltage applications, the current ripple, the size of the inputfiltering capacitor and electromagnetic interference. A specific singleswitch modulation technique is used: The modulation signal is appliedonly on one transistor at each sequence of operation defined by therotor position detector. The other transistor is switched on during allthe duration of this sequence of conduction. This single switchmodulation method maximizes the efficiency of the electronic supply andthe current regulation is realized without any external current sensor.

According to the above features, from a broad aspect, the presentinvention provides a brushless DC motor for electrical vehiclemotorization. The motor comprises a cylindrical rotor with 22 polesconstructed with segments of permanent magnet material alternativelymagnetized north and south. A stator core of ferromagnetic material isspaced inwardly of the rotor and defines a magnetic clearance gaptherebetween. The stator core has twenty four slots and define teethbetween the slots. A three-phase winding with coils of insulated wire iswound around the teeth. There is provided two coils per slot havingpredetermined connection patterns C, C′, C, C′, B′, B, B′, A′, A, A′, A,A′, C′, C, C′, B′, B, B′, B, B′, A′, A, A′, C′.

According to a still further broad aspect of the present invention thereis provided a brushless DC motor electronic pulse with modulation driverand control system. It includes a power electronic three phase inverterhaving six power of MOSFETs. A current control system is coupled to theinverter for generating a 120 electrical degrees rectangular phasecurrent pulses. An electronic control system is provided for both motorand a generator operation mode of the motor and uses a single switchmodulation technique.

According to a still further broad aspect of the present invention thereis provided a brushless DC motor for breaking a wheel of devices onwhich people are displaced by self-motorization or electric motormotorization. The motor comprises a cylindrical rotor with twenty twopoles constructed with segments of permanent magnet materialalternatively magnetized north and south, a stator core of ferromagneticmaterial spaced inwardly of said rotor and defining a magnetic clearancegap, therebetween said stator core having twenty-four slots and definingteeth between said slots, a three phase winding with coils of insulatedwire being wound around the teeth. The rotor is connected to a hub ofthe wheel. Control circuit means is provided to control the torque ofthe motor and therefore its arresting force.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a brushless DC motor structureincluding a motor, a power electronics system and a current controlsystem;

FIG. 2 is a diagrammatic view of the twenty-two pole rotor and thetwenty-four slot stator arrangement in accordance with principles of thepresent invention;

FIG. 3 is a coil winding arrangement with two coils per slot;

FIG. 4 indicates the position of the three Hall sensors in the motorwhich are used to detect the rotor position;

FIG. 5 is a simplified diagram of the electronic system (powerelectronics system (inverter) and control system);

FIG. 6 shows the conduction sequence order of the power MOSFETs;

FIG. 7 shows the rectangular waveform of the phase current which is inphase with the waveform of the back electromotive force (back emf) ofthe same phase;

FIG. 8 shows the diagram of the MOSFET control signals during one periodof the motor operation mode;

FIG. 9 indicates the current flow in the case of the sequence (T1-T2) inmotor operation mode;

FIG. 10 is a diagram of the MOSFET control signals during one period ofthe generator operation mode;

FIG. 11 indicates the current flow in the case of the sequence (T1-T2)in generator operation mode;

FIG. 12 shows a schematic view of the current control;

FIG. 13 is a schematic diagram of the transformation of the signals ofthe rotor position sensors and the generation of the MOSFET gate controlsignals in motor operation mode;

FIG. 14 is a schematic diagram of the electronic system for thegeneration, the MOSFET gate control signals, and the measurement of thephase current in the motor and generator operation mode with the singleswitch modulation technique, and

FIG. 15 is a simplified fragmented side view showing the motor of thepresent invention coupled to a wheel of a bicycle through its rotor.

DETAILED DESCRIPTION OF THE INVENTION

In electrical vehicle applications, it is necessary to produce highstarting torque and to ensure variable speed in both motor and generatormodes of operation. The use of a brushless DC motor is particularly welladapted to this kind of applications. To reduce the cost of theelectronic system and the number of sensors, it is better to supply themotor winding phases with a rectangular waveform current. The motortorque is controlled by a simple current regulation and the phasevoltage is chopped with a pulse width modulation technique (PWM). Theschematic diagram of this kind of brushless DC motor is presented onFIG. 1. It includes a permanent magnet motor 10, a power electronicsupply 11, a rotor position detector 12, a current measurement system 13and a current regulation system which is comprised of a current controlcircuit 14 fed by the current measuring circuit 13 and a torquereference or current reference circuit 16. The current control circuit14 is connected to the power electric supply circuit 11 to control thetorque of the motor 10. The system can be used for motor or generatoroperation with energy recuperation on the battery 15 during brakingperiods.

As shown in FIG. 2, the proposed solution in the present invention is touse a motor 10 structure having a twenty-two poles and twenty-four slots18 with a cylindrical outer rotor 19. Permanent magnets 20 are mountedon the rotor inner surface 21 and alternatively magnetized north andsouth. The high number of poles reduces the iron volume and providesacceptable iron losses when the speed is less than 1,000 rpm.

As shown in FIG. 3, a concentrated winding 22 is wound around the teeth23. The advantages of a concentrated winding around the teeth incomparison with a classical distributed winding are described in KonecnyU.S. Pat. No. 4,774,428 and the article reference E.M.I. tests on abrushless actuator: Comparison of different operation modes by J. Cros,S. Astier, J. M. Vinassa, M. Lajoie-Mazenc and J. P Berry published inEuropean Power Electronics in September 1993. The volume of copper isreduced and subsequently the Joule losses are minimized. The energyefficiency and the motor starting torque per unit volume of winding aremaximized.

In the embodiment shown in FIG. 2 and FIG. 3, an additional two coils(7) per slot (18) are shown with predetermined connection patterns asfollows: C, C′, C, C′, B′, B, B′, A′, A, A′, A, A′, C′, C, C′, B′, B,B′, B, B′, A′, A, A′, C′, wherein an apostrophe after a letterrepresents a counterclockwise winding direction and a letter without anapostrophe represents a clockwise winding direction and wherein eachletter represents one phase of the motor. This results in reduced torqueripple without any slot or magnet skewing. This connection pattern isreferred to as a “5-3 pattern”. A mutual inductance between the phasesof the stator has a value which corresponds to roughly one half of thevalue of the inductance of each phase.

A winding configuration with two coils per slots is presented on FIG. 3and it can be used for the proposed motor structure (windingcoefficient: 0.941). As shown in FIG. 4, Hall sensors or detectors 24are placed to position the phase current and the phase electromagneticforce (back emf) waveforms like in FIGS. 7 & 8. The maximum value of thetorque to current ratio is then obtained with this configuration.

The cogging torque ripple are greatly reduced without any slot skewing,as in the other structure combinations described by Konecny U.S. Pat.No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al.U.S. Pat. No. 4,719,378. The least common multiple (LCM) of the motor'spoles and slots describes how many peaks of cogging torque will bepresent over a single revolution of the motor. In this case, there are264 torque pulses per revolution and consequently, the cogging torqueamplitude is very low (less than 3% of the rated torque). The proposedmotor structure also minimizes the net radial force like anotherstructure described by Huang and al. U.S. Pat. No. 5,675,196.

Referring now to FIG. 5 there is shown the electronic supply whichincludes a power electronics system and a low power control electronicssystem. Both systems can be inserted in the cavity 26 inside the motorhousing, in the center if the stator yoke 27. The power electronicssystem is a six switches, PWM (pulse width modulation) inverter 26. Sixtype N MOSFETs 28 (T1, T2, T3, T′1, T′2, T′3) are used and the structurediodes of the MOSFETs 29 are used to ensure the current reversibility.The electronic system also includes a push-pull driver 30 for eachMOSFET, three boostrap supplies 31 feed the driver stages of the threetransistors T′1, T′2, T′3 of the upper side of the inverter 28 and threelevel-shift control signals are applied to the driver stages oftransistor T′1, T′2, T′3.

A current regulation circuit 32 generates a PWM signal at eachtransistor control signal. The voltages of the power MOSFETs 29′ T1, T2,T3 on the lower side 28′ of the inverter 28 are used to measure themotor currents. The rotor position sensors 24 define the conductionsequence order and are also used to select the voltage of the powerMOSFET 29 in conduction to be sensed by means of a multiplexer 33 with 3inputs 33′ and 1 output 33″. The multiplexer 33 is used to generate asignal equivalent to the motor current, which can be used in the currentregulation loop. The operator can select the operation mode of thesystem (motor or generator operation mode) and the current referencelevel to impose the torque of the machine.

FIG. 6 presents the chronogram 37 of the conduction sequences of thepower MOSFETs 29. At each time, there are only tow MOSFETs switched on.There are six sequences of operation in an electric period . During eachsequence two phases of the machine are supplied. There are six currentcommutations when the rotor rotates with an angle of 32.7 degrees. Thecommutation process is controlled by the rotor position detectors 24(i.e. Hall sensors).

FIG. 7 shows the rectangular waveform 38 of the phase current which isin phase with the waveform 39 of the back electromotive force (back emf)of the same phase.

Referring now to FIGS. 8 to 11, there is shown a single switchmodulation technique used for both motor and generator operation. Themodulation signal is only applied on the gate of the transistors of theinverter upper side (T′1, T′2, T′3) in the case of motor operation mode(see FIGS. 8 & 9). The transistors T1, T2, T3 remain switched “on”during all the duration of the conduction sequence. In comparison to theclassical modulation technique where the modulation signal is applied toswitches of both lower and upper sides. This specific single switchmodulation technique provides lower commutation losses and lowerconduction losses in the case of low voltage applications (the voltagedrop of a power MOSFET is lower than the voltage drop of a diode) seethe E.M.I. tests article referred herein. The efficiency of the inverter28 is higher. This single switch modulation technique simplifies themeasurement of the phase currents and it eliminates the need of anexternal current sensor. The voltage of the MOSFETs (T1, T2, T3) of theinverter lower side 28′ can be used to measure the motor phase currentsduring all the sequences. In the case of the sequence T′1-T2, thevoltage of transistor T2 is used to measure the motor phase current.

FIG. 8 shows the control signals which are applied to the transistorgates in the case of the single switch modulation technique.

FIG. 9 shows the current flow during one sequence in the motor operationmode. When transistors T′1 and T2 are switched “on” (FIG. 9 a), thebattery supplies two phases 40 and 41 of the motor. When the transistorT′1 is switched “off”, the structure diode of MOSFET T1 is switched “on”and a free wheeling operation is occurring (FIG. 9 b). The currentripple is reduced by half in comparison with the classical two-switchmodulation technique. There is no current inversion in the DC bus and sothe size of the filtering capacitor (not shown but well known in theart) can be reduced (lower RMS current on the DC bus). Consequently, theelectromagnetic interferences are also lower than in the case of theclassical modulation mode see E.M.I. article referred herein.

FIGS. 10 & 11 present the case of the generator operation mode. Theupper side inverter transistors 29 T′1, T′2, T′3 are all switched “off”during the generator operation mode. Only the structure diodes of thesetransistors are used in this mode. A modulation signal is applied on thegate 42 of transistors T1, T2, T3 (see FIG. 5) in the lower side 28′ ofthe inverter 28. There are some intervals where permanent conduction isoccurring. They are used to measure the MOSFET voltage for the currentcontrol (see FIG. 11). FIG. 11 shows the current flow during onesequence of operation. The machine or motor current increases when thetransistors 30 T1, T2 are switched “on” (FIG. 11 b). When transistor T1is switched “off”, the structure diode of transistor T′1 is switched“on” and the machine supplies the battery 43 (FIG. 11 a).

FIGS. 12 and 13 show block diagram views of a classical currentregulation with a PI regulator 44 which can be applied in the case ofthe single switch modulation mode. The proposed electronic system forboth motor and generator operation modes with the single switchmodulation technique is presented on FIG. 14. This system includes twosignal multiplexers and several AND/OR gates used to control the signalsapplied to the transistor driver stages and the signals of measurementsof the machine current. The system is also realizable by an integratedcircuit or a programmable circuit obvious to a person skilled in theart.

Referring now to FIG. 15 there is shown a brushless DC motor 50,constructed as above described, and wherein the rotor 51 is connected toa hub 52 of a wheel 53 herein a bicycle wheel. Alternatively, to reduceproduction cost, the motor cover housing may have connections to whichthe spokes of the wheel are connected to. A battery, not shown, isconveniently secured to the bicycle and power is fed to the controlcircuitry provided or mounted within the cavity inside the stator. Acable 54 is secured to a control device which is operated by the user ofthe bicycle to control the speed of the motor. This control device couldbe in the form of a rotating handle and grip, a hand lever device or anyother convenient means. When the motor is used as a motorizing machineit drives the wheel 53. The motor can also be utilized as a brake whenplaced in its generating mode. As previously mentioned, this motor canbe secured to all sorts of electrical vehicles such as wheel chairs,scooters, tricycles, golf trolleys, small utility vehicles etc.

It will be understood that numerous modifications thereto will appear tothose skilled in the art. Accordingly, the above description andaccompanying drawings should be taken as illustrative of the inventionand not in a limiting sense. It will further be understood that it isintended to cover any variations, uses, or adaptations of the inventionfollowing, in general, the principles of the invention and includingsuch departures from the present disclosure as come within known orcustomary practice within the art to which the invention pertains and asmay be applied to the essential features herein before set forth, and asfollows in the scope of the appended claims.

1. A brushless DC motor/generator (10) comprising; a cylindrical outerrotor (19) with twenty two magnetically coupled poles (20) constructedwith segments of permanent magnet material alternatively magnetizednorth and south, a stator having a core (8) of ferromagnetic materialspaced inwardly of said rotor and defining a magnetic clearance gap (9)therebetween, said stator core having twenty-four slots (18) anddefining teeth (23) between said slots (18), a three phase winding withcoils (7) of insulated wire being wound around the teeth, there beingmutual inductance between the phases of said stator, an electronicsupply (11) including a power electronics system and a current controlcircuit means (14) to control the torque of said motor (10) andtherefore its arresting force for braking a wheel (53) of devices onwhich people are displaced by said DC motor motorizing said wheel,further comprising an additional two coils (7) per slot (18) withpredetermined connection patterns: C, C′, C, C′, B′, B, B′, A′, A, A′,A, A′, C′, C, C′, B′, B, B′, B, B′, A′, A, A′, C′, resulting in reducedtorque ripple without any slot or magnet skewing, and wherein themagnetic path of flux produced by each phase current is not independent.2. A brushless DC motor/generator (10) as claimed in claim 1 furthercomprising a multiple combination of additions of the number of saidtwenty-two poles and said twenty-four slots (18), including forty-foursaid poles and forty-eight said slots, or sixty-six said poles andseventy-two said slots or ninety-six said poles and eighty-eight saidslots; and a wound winding (7) around said teeth (23) with one of eitherone coil per slot or two coils per slot.
 3. A brushless DCmotor/generator (10) as claimed in claim 1 further comprising three Hallsensors (24) mounted near said air gap (25) at predetermined positionsand fixed to or beside some of said teeth (23).
 4. A brushless DCmotor/generator (10) as claimed in claim 1 further comprising a powerelectronics pulse width modulation driver (30), said pulse widthmodulation driver (30) having a three phase inverter (28) including sixpower MOSFETs (29), said current control system (32) being coupled tosaid inverter (28) for generating 120 electrical degrees rectangularphase current pulses, said control system (14) using a single switchmodulation technique.
 5. A brushless DC motor/generator (10) as claimedin claim 4 characterized in that said single switch modulation techniquecomprises three of said MOSFETs (30) being connected as an upper side ofsaid inverter (28) and remain switched “on” by a modulation signalduring a motor operation mode of said motor (10), three others of saidMOSFETs (30) being connected as a lower side of said inverter (28) andused to measure motor phase currents during all sequences of the MOSFETsof said upper side.
 6. A brushless DC motor/generator (10) as claimed inclaim 5 characterized in that said MOSFETs (30) of said upper side ofsaid inverter (28) are switched “off” during a generator operation modeof said DC motor (10), and wherein a modulation signal is applied on agate of said three MOSFETs on said lower side of said inverter.
 7. Abrushless DC motor/generator (10) as claimed in claim 1 characterized inthat said motor (10) is also used as a wheel braking device when used ina generator mode, said rotor (19) being connected to a hub (52) of awheel (53) powered by said motor (10) when in a motorized mode.
 8. Abrushless DC motor/generator (10) as claimed in claim 4 characterized inthat voltages across said MOSFETs (30) on a lower side of said inverter(28) are used to generate a current measurement for the purpose of motorcurrent control of said single switch modulation technique.